136 



Mr. D. Forbes's Researches on the 



And it may be remarked that a microscopic examination of the 

 peridote found in aerolites reveals a very distinct structure, 

 altogether characteristic of the same, and differing from that of 

 the olivine found in other rocks. 



(2) Mineral Products of Volcanic Action. 

 As what may be called primary minerals are found: — 



Pyroxene. 







Sulphur. 



Olivine. 







Chloride of iron. 



Anorthite*. 







Sulphurous acid. 



Quartz. 







Sulphuric acid. 



Pumice. 







Boracic acid (sassolin). 



Obsidian. 







Hydrochloric acid. 



nd as secondary minerals : — 





Alum. 



Gibbsite. 





Iron glance. 



Soda alum. 



Hayesine. 





Hsematite. 



Copperas. 



Gypsum. 







(3) Minerals of the recent or Unconsolidated Surface- deposits 



Soda alum. 



Gypsum. 





Quartz. 



Astrakanite. 



Iron-pyrites. 





Fossil resin. 



Calcite. 



Limonite. 





Sal-ammoniac. 



Copperas. 



Natron. 





Salt. 



Epsomite. 



Nitratine. 





Thenardite. 



Glauberite. 



Nitre. 





Trona. 



Glauber-salt. 



Pickei 



-ingite. 





Vivianite. 



Many of which, as it will be perceived, occur as saline effervescences 

 on soils at one time covered by the sea. 



(4) Minerals composing the Beds of the Tertiary Formations. 



In these formations, besides lignite, sphserosiderite, calcite, 

 and iron -pyrites, few mineral substances are found in a suffi- 

 ciently pure state to be considered true species; and the whole 

 mass can only be regarded as the result of the wearing down of 

 rocks of a previous age. 



(5) Minerals of the Post -Cretaceous Basaltic Dykes. 



These rocks have a strong general resemblance to the basalts 

 of the Giant's Causeway in Ireland, and, like that, are generally 

 so compact as only to allow of their components being distin- 

 guishable by the assistance of the microscope. It is there- 

 fore uncertain what exact felspars they may contain ; but in 

 some cases Labradorite has been made out with certainty, along 

 with augite or hypersthene, and a magnetic mineral the character 



* The felspars occurring in these volcanic rocks have not yet been 

 studied. 



